The present invention relates to compressors and particularly relates to apparatus for repairing or upgrading components in compressors.
In axial flow compressors, stator vanes alternate with rotating blades or buckets in the various stages of the compressor. The stator vanes are circumferentially spaced one from the other about the compressor axis and are secured to the upper and lower compressor casing halves. The upper and lower casing halves are joined one to the other at the compressor midline and provide a complete circumferential array of stator vanes for each compressor stage. As each rotating blade mounted on the rotor completes each revolution at a given rotational velocity, the rotating blade receives aerodynamic excitation pulses from each stator vane. This pulse can be generated from the wake of the upstream stator vane or the bow wave of the downstream stator vane. It is also possible to generate excitations in the rotating blade from differences between the upstream and downstream stator vane counts. These pulses induce a vibratory response in the rotating blade that can be deleterious to the rotating blade causing failure due to high cycle fatigue.
Typically the stator vane or blade count in the upper and lower halves of the compressor casing for a given stage are equal in number to one another. For example, in an initial stage S0 of a given compressor, the blade count for the stator vanes in each of the upper and lower compressor casing halves may be 24/24. In the next stage S1, the blade count may be 22/22. The first number represents the number of stator vanes in the upper casing half and the second number represents the number of stator vanes in the lower casing half of the same stage. The total stator vane count in S0 and S1 is therefore forty-eight and forty-four stator vanes respectively. However, because of the vibratory responses of the rotating blades, non-uniform vane spacings between upper and lower casing halves have been used in the past. Thus, different and alternative upper and lower blade counts in succeeding stages have been provided to reduce or eliminate the vibratory response. For example, in one compressor, stages S0 and S1 have had vane counts of 24/23 and 23/24, respectively. These non-uniform blade counts have been used in original equipment manufacture.
There are, however, a significant number of compressors in use in the field where there is an equal number of stator vanes in the upper and lower compressor halves for given stages. Certain other compressors in the field have an unequal number of stator vanes in the upper and lower compressor halves with adjacent stages, e.g. S0 and S1, having equal numbers of blades but alternate blade counts between the upper and lower halves of the compressor casing. Changing blade counts in the field was not previously considered practical since costly removal of the rotor in the field was required.
Because the rotor is closely fitted to the middle and aft (or rearward) sections of the compressor, it is geometrically difficult to reach the areas where the blades reside or to drill, tap, and counter-bore load dam pin holes in the area desired. Additionally, the current known methods for removal of these blades increase the likelihood that the rotor, stator blades or adjacent hardware may be damaged during the removal process. Moreover, the extended reach and limited access to the stator blades being removed underneath the rotor and rotor blades creates an ergonomic issue potentially leading to operator injury.